History of Rockets: Japanese Rockets

Ethan Wong

April 28, 2023

Lambda 4S was one of the first rockets used by Japan and helped the country put a satellite in Earth’s orbit with the use of their own rocket. There were many complications with Japan building rockets in the 1950s with the end of WWII, yet negotiations were made to confirm that the Lambda rocket would not be used as a ballistic missile in any way. To accomplish this, Lambda was forbidden to use any sort of guidance system until necessary to put the rocket into space; engineers added fins onto the four-stage rocket to help the vehicle guide itself without turning and then used a diagonal launching pad to get the rocket in the correct starting trajectory (rocket wasn’t launched straight up like typical rockets). Once the first two stages lifted Lambda into the atmosphere, the air became too thin for the fins to keep the rocket stable, so the third stage utilized spin stabilization. The fourth stage stops spinning and the rocket is re-oriented before spinning and starts again to place the payload in orbit. After 5 attempts at launch, the Lambda rocket successfully made it into the Earth’s orbit, making Japan the 4th country to use its rocket to put a satellite into orbit. 

The Mu rockets were the next generation of rockets developed by Japan and used eight strap-on boosters (SB-310) to help increase thrust. Mu-3C was the first iteration of the Mu rockets to have an improved guidance system that allowed for only 3 stages. Yet, the first stage still used fins to help with the flight, along with the weird launch angle. The Mu-3H had a longer first stage than the Mu-3C and achieved thrust vectoring (example of thrust vectoring: gimbaled LR-87 engines on Titan II) on its first stage; the Mu-3H rocket launched three times. Mu-3SI was very similar to the Mu-3H and the Mu-3SII had two strap-on boosters that replaced the eight SB-310 engines on the first stage The M-V rocket was the last variation of the Mu rockets which launched 8 times. It had 3 stages and no fins on the rocket at all, yet still kept the angled-launch pad. 

The H-I rocket was the next design to come out of Japan and had 9 total successes and had a similar first-stage design to the Delta rockets. The second stage would use a LE-5 engine and the third stage could be used for certain payloads. The H-II rocket is one of the most reliable rockets designed by Japan. It features a LE-7 engine on the first stage powered by liquid hydrogen and LOX, as well as a LE-5A engine for the second stage. Improvements were made to the LE-5A engine to make it re-ignitable based on the H-I rocket’s LE-5 engine. The first stage is assisted with two strap-on boosters. The H-II first launched on February 3rd, 1994, and had 7 launches. The newly designed H-3 rocket launched for the first time on March 6/7th, 2023 after a scrubbed launch back in February. The rocket launched with dual LE-9 engines on the first stage and was equipped with two strap-on boosters. However, other variations can be made with up to four strap-on boosters and three LE-9 engines for extra thrust and power during launch. Sadly, the rocket exploded during its debut launch, and a future article will discuss this malfunction in greater detail.